Old home hardwoods directly onto joists

I have a 125 year old house in mo and found on the third floor there is 1 inch thick x 3 and 1/4 tongue and groove (oak???) under the carpet that I removed in one room. I assume this runs throughout the third floor under the carpet. The floor runs the opposite way as the joists and is nailed directly into the joists with old square head long nails. I have to replace a couple broken boards but otherwise the flooring would look good after a sanding.



Since its on the third floor and I don't have the moisture or temp issues, am I ok with refinishing it or could it just be an old subfloor?j

Old home hardwoods directly onto joists